128 research outputs found
New g'r'i'z' Photometry of the NGC 5128 Globular Cluster System
We present new photometry for 323 of the globular clusters in NGC 5128
(Centaurus A), measured for the first time in the filter system. The
color indices are calibrated directly to standard stars in the
system and are used to establish the fiducial mean colors for the blue and red
(low and high metallicity) globular cluster sequences. We also use
spectroscopically measured abundances to establish the conversion between the
most metallicity-sensitive colors (, ) and metallicity,
[Fe/H].Comment: 14 pages, 9 figures, accepted in A
Scrutinizing public expenditures: assessing the performance of public accounts committees
In 2002, David McGee wrote a comprehensive report on two important elements in the system of public financial accountability, namely the office of the Auditor General and the parliamentary oversight committee commonly referred to as the Public Accounts Committee (PAC). The purpose of the present paper is to deepen McGee's analysis of PACs. In particular, the authors define PAC success and identify those factors that affect PAC peformance. They use data that were collected by the World Bank Institute in 2002, when a survey questionnaire was sent to 51 national and state/provincial parliaments in Commonwealth countries in Asia and Australasia, and Canada and the United Kingdom. The authors find that the institutional factors which most account for the success of the PACs are the focus on government's financial activity rather than its policies, the power to investigate all past and present government expenses, the power to follow up on government action in response to its recommendations, and its relationship with the Auditors General.National Governance,Parliamentary Government,Politics and Government,Business Environment,Business in Development
Radial Velocities of Newly Discovered Globular Clusters in NGC 5128
We present radial velocity measurements for 74 globular clusters (GCs) in the
nearby giant elliptical NGC 5128, of which 31 are newly discovered clusters.
All the GC candidates were taken from the list of possible new clusters given
in the Harris, Harris, & Geisler (2004) photometric survey. In addition to the
newly confirmed clusters, we identified 24 definite foreground stars and 31
probable background galaxies. From a combined list of 299 known GCs in NGC 5128
with measured radial velocities and metallicity-sensitive (C - T_1) photometric
indices, we construct a new metallicity distribution function (MDF) for the
cluster system. The MDF shows an approximately bimodal form, with centroids at
[Fe/H] = -1.46 and -0.53, and with nearly equal numbers of metal-poor and
metal-rich clusters in the two modes. However, there are many
intermediate-color clusters in the distribution, and the fainter clusters tend
to have a higher proportion of red clusters. These features of the MDF may
indicate a widespread age range within the cluster system as well as an
intrinsically broad metallicity spread.Comment: 10 pages, 7 figures, 4 tables - accepted in Astronomical Journa
Rainfall Estimations From Geosynchronous Satellite Imagry
A method to estimate rainfall from visible geosynchronous satellite images is outlined. The two component relationships, derived from ATS-3 and WSR-57 radar data, are discussed. Calculations are made on two days with this method and compared with ground truth rainfall. Satellite estimates on both days are within a factor of two of ground truth.
Sources of error in the component relationships are ennumerated. Several planned refinements, such as stratification of the data by synoptic condition and origin of convection, are presented
Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128
We investigate the shallow increase in globular cluster half-light radii with
projected galactocentric distance observed in the giant galaxies M87,
NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the
effects of orbital anisotropy and tidally under-filling clusters. While a
strong degeneracy exists between the two parameters, we use kinematic studies
to help constrain the distance beyond which cluster orbits become
anisotropic, as well as the distance beyond which clusters are
tidally under-filling. For M87 we find kpc and kpc and kpc.
The connection of with each galaxy's mass profile indicates the
relationship between size and may be imposed at formation, with only
inner clusters being tidally affected. The best fitted models suggest the
dynamical histories of brightest cluster galaxies yield similar present-day
distributions of cluster properties. For NGC 5128, the central giant in a small
galaxy group, we find kpc and kpc. While we
cannot rule out a dependence on , NGC 5128 is well fitted by a tidally
filling cluster population with an isotropic distribution of orbits, suggesting
it may have formed via an initial fast accretion phase. Perturbations from the
surrounding environment may also affect a galaxy's orbital anisotropy profile,
as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer
NGC 5128 clusters remain isotropic.Comment: 16 pages, 7 figures, 4 tables, Accepted for publication in MNRA
Adult Human Keratinocytes Migrating over Nonviable Dermal Collagen Produce Collagenolytic Enzymes That Degrade Type I and Type IV Collagen
Human adult keratinocytes migrating on a nonviable dermal substrate in cultures without fibroblasts induce thinning and degradation of the collagen substrate beneath the migrating epithelium. Further, unconcentrated conditioned medium from the cultures exhibit collagenolytic activity against both type I and type IV collagen which is inhibited by EDTA but not by phenylmethylsulfonyl fluoride or N-ethylmaleimide. Since the migrating epithelium and dermal substrate do not contain fibroblasts, this study shows that migratory keratinocytes in contact with interstitial collagen are capable of producing collagenases against type I and type IV collagen. Moreover, migratory keratinocytes appear to be similar to highly metastatic cells in their ability to degrade basement membrane collagen
The Kinematics of the Globular Cluster System of NGC 5128 with a New, Large Sample of Radial Velocity Measurements
New radial velocity measurements for previously known and newly confirmed
globular clusters (GCs) in the nearby massive galaxy NGC 5128 are presented. We
have obtained spectroscopy from LDSS-2/Magellan, VIMOS/VLT, and Hydra/CTIO from
which we have measured the radial velocities of 218 known, and identified 155
new, GCs. The current sample of confirmed GCs in NGC 5128 is now 605 with 564
of these having radial velocity measurements. We have performed a new kinematic
analysis of the GC system that extends out to 45 arcmin in galactocentric
radius. We have examined the systemic velocity, projected rotation amplitude
and axis, and the projected velocity dispersion of the GCs as functions of
galactocentric distance and metallicity. Our results indicate that the
metal-poor GCs have a very mild rotation signature of (26 pm 15) km/s. The
metal-rich GCs are rotating with a higher, though still small signature of (43
pm 15) km/s around the isophotal major axis of NGC 5128 within 15 arcmin. Their
velocity dispersions are consistent within the uncertainties and the profiles
appear flat or declining within 20 arcmin. We note the small sample of
metal-rich GCs with ages less than 5 Gyr in the literature appear to have
different kinematic properties than the old, metal-rich GC subpopulation. The
mass and mass-to-light ratios have also been estimated using the GCs as tracer
particles for NGC 5128. Out to a distance of 20 arcmin, we have obtained a mass
of (5.9 pm 2.0) x 10^(11) M_(sun) and a mass-to-light ratio in the B-band of 16
M_(sun)/L_(B,sun). Combined with previous work on the ages and metallicities of
its GCs, as well as properties of its stellar halo, our findings suggest NGC
5128 formed via hierarchical merging over other methods of formation, such as
major merging at late times.Comment: Accepted for The Astronomical Journal, 14 pages plus 12 figures and 7
table
Using Coupled Eulerian and Lagrangian Grids to Model Explosive Interactions with Buildings
This paper presents the development of a computational model that can be used to study the interactions between structures and detonating explosives contained within them. This model was developed as part of an effort to develop a rubble characterization model for use in AmmoSIM, an agent based urban tactical decision aid (UTDA) software for weapon-target pairing. The rubble pile created following the collapse of a building in a combat situation can significantly impact mission accomplishment, particularly in the area of movement and maneuver. The information provided by AmmoSIM will enable both platoon level and command center staff to make informed decisions concerning urban attack tactics.
Computational models were created using a combination of AUTODYN 2D and 3D. The detonation was modeled using a 2D wedge, which is a common method used in AUTODYN. The information obtained from the wedge calculation was then written to a data file and subsequently remapped into a larger 3D Euler air grid. The air grid loaded with blast pressure information was coupled to interact with the Lagrangian building parts. The Riedel, Hiermaier and Thoma (RHT) Concrete Model from the AUTODYN material library was utilized to create the components of the building. Results of the latest models will be given. Additionally, the paper details the development of the model at length including topics such as grid sizing, computational cost comparisons, grid interactions, multi-solver coupling, strain erosion, and material parameters and selections
The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
We present new integrated light spectroscopy of globular clusters (GCs) in
NGC 5128 in order to measure radial velocities and derive ages, metallicities,
and alpha-element abundance ratios. Using Gemini-S 8-m/GMOS, we obtained
spectroscopy in the range of ~3400-5700 AA for 72 GCs with S/N > 30 /AA and we
have also discovered 35 new GCs within NGC 5128 from our radial velocity
measurements. We measured and compared the Lick indices from HdeltaA through
Fe5406 with the single stellar population (SSP) models of Thomas et
al.(2003,2004). We also measure Lick indices for 41 Milky Way GCs from Puzia et
al. (2002) and Schiavon et al. (2005) with the same methodology for direct
comparison. Our results show that 68% of the NGC 5128 GCs have old ages (> 8
Gyr), 14% have intermediate ages (5-8 Gyr), and 18% have young ages (< 5 Gyr).
However, when we look at the metallicity of the GCs as a function of age, we
find 92% of metal-poor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8
Gyr, indicating that the majority of both metallicity subpopulations of GCs
formed early, with a significant population of young and metal-rich GCs forming
later. Our metallicity distribution function generated directly from
spectroscopic Lick indices is clearly bimodal, as is the color distribution of
the same set of GCs. Thus the metallicity bimodality is real and not an
artifact of the color to metallicity conversion. The [alpha/Fe] values are
supersolar with a mean value of 0.14pm0.04, indicating a fast formation
timescale. However, the GCs in NGC 5128 are not as [alpha/Fe] enhanced as the
Milky Way GCs also examined in this study. Our results support a rapid, early
formation of the GC system in NGC 5128, with subsequent major accretion and/or
GC and star forming events in more recent times (abridged).Comment: Accepted to The Astrophysical Journal, 36 pages, 14 figures, 7 table
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